Chibiusa and Usagi by Imouto Kitten.

Tsukino Ikuko let out a sigh as she heard a crash followed by a pair of 
female voices arguing. It had only been a few days since she first took 
in her niece, but already, the constant bickering between the adorable 
little pinkette and her own daughter was getting old.

Sitting down the dish she was washing, Ikuko dries her hands and puts on 
her best "you've been bad and should feel bad" face before stepping out 
of the kitchen and into the living room to find the pair of 
odango-headed girls wrestling with one another, seemingly oblivious to 
the destruction around them.

Raising her voice to be heard over whatever the pair are shouting at 
each other, Ikuko cries out, "Break it up, you two!"

Almost immediately, the pair halt their fight to sit on their heels, 
both looking chastised yet still giving each other scornful glances, 
lightning flashing whenever their eyes meet.

"I don't know what you girls were fighting over, and I realy don't care, 
but this is no way for cousins to behave!" Turning to glare specifically 
at her daughter, she adds, "And Usagi, you're more than twice Chibiusa's 
age, you should be setting a better example." Clapping her hands as if 
to declare the matter settled, Ikuko declares, "Now, I want you two to 
clean up this mess... and then I want the two of you to take a bath 
together."

"Together!?" the pair cry in outrage, "with her!?" pointing at each 
other.

"Yes, maybe some skinship while soaking in a hot, relaxing bath will 
help you two bond and mellow out around each other." declares the 
physically older woman before turning her back on them and heading back 
to the kitchen to finish the dishes.

Despite constantly giving each other dirty looks, it doesn't take long 
for the pair to clean the living room and make their way to the 
bathroom.

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However, as the pair start undressing for their bath, the diminutive 
time traveller grows a bit self-conscious, especially upon seeing the 
blonde's near supermodel physique minus her serafuku, the pinkette's 
biggest secret after her true identity and being from the future 
starting to tent her skirt.

As Chibiusa tries to adjust her skirt to conceal the quickly growing 
problem, Usagi notices her unwelcomed houseguest has only removed her 
blouse.

"Hey, I don't want to take a bath with you anymore than you want to take 
one with me, but Mama won't be happy if we don't do as she says." 
declares the teen as she reaches for the pinkette's waistband.

"NO!" yells Chibiusa, trying to dodge Usagi's grabby hand, only for her 
to trip over her own feet, letting Usagi reach her target and yank both 
Chibiusa's skirt and panties to her ankles.

Chibiusa's face goes pink as her hair and Usagi's eyes go big as saucers 
and she starts to drool as Chibiusa's secret is revealed, namely a very 
erect penis easily a foot long and as thick as Usagi's wrist.

"Wa-wait, you're a boy?!" shouts Usagi once her brain manages to reboot.

Standing up and kicking her clothes aside, Chibiusa stomps her foot as 
she declares, "No, I'm a girl!" Lifting up her girlcock and pointing at its 
base, "See, I still have a cunny and everything!"

But Usagi isn't really listening, the sight of that magnificent member 
driving all thoughts beyond, 'Me likey cock.' from her mind, even 
thoughts of how Mamoru recently dumped her out of nowhere.

Crawling over to Chibiusa and looking damn sexy in the process, Usagi 
practically purrs as she declares, "That's a yummy looking cock you have 
there, cutie." and before Chibiusa can react, she finds Usagi's lips 
wrapped around her tip and Usagi's breasts wrapped around her shaft. The 
pinkette can't help letting out a moan and her knees tremble as Usagi 
proves herself to be a natural born slut, twirling her tongue around 
Chibiusa's tip as those marshmallowy tits caress her shaft.